A transducer consists of a piezo crystal which can generate an ultrasonic sound wave by means of an electrical voltage and can, conversely, transform such an ultrasonic sound wave into a voltage. In medical echography, transducers are incorporated in a transducer element in one or more rows in order to transmit ultrasonic sound waves into the body of a human or an animal and receiving the reflection of these rays in order to be able to compose an image of the inside of said human or said animal.
To this end, such a transducer element is coupled to an echoscope by means of a connector, which echoscope ensures that the sound waves to be transmitted are generated by the transducers and which receives the measured values of the reflection via the transducer element and processes these to form images which can be interpreted by the user (usually medically qualified staff).
By means of an echoscope and a suitable transducer element, it is then possible, for example, to image a blood vessel into which a needle has to be inserted.
At present, there are various types of transducer elements on the market, each of which is suitable for specific applications.
In a linear transducer element, transducers are arranged in a row. By means of such a linear transducer element, sound waves are transmitted into the tissue parallel to one another and the echoscope generates a rectangular image by measuring the reflection. In this case, the image width and the line density remain constant at every tissue depth. Such a transducer element results in a high resolution close to the transducers. A transducer element of this type is, for example, ideal for use in diagnosing soft tissue. However, curved skin surfaces quickly cause cast shadows which impede correct imaging.
A sector transducer element produces a conical image which is very narrow close to the transducer element and becomes wider at increasing tissue depth. With such a transducer element, ribs, for example, do not produce disruptive cast shadows, so that this type of transducer element is often used in cardiology and abdominal. The frequency of these transducers is low in order to be able to carry out deep scans, but a lower frequency also lowers the resolution. In this case, however, the structures in the vicinity are not imaged well and the line density decreases with the tissue depth.
A convex transducer element is a compromise between such a linear transducer element and a sector transducer element.
However, the drawback of such transducer elements with a single row of transducers is that, for example, a needle which has to be imaged with these, either has to be axially imaged or in the longitudinal direction. Using an axial view produces the best overview, but results in such a needle only being shown as a dot on the screen. In the longitudinal direction, on the other hand, it is more difficult to gain a good overview of the surrounding structures, but such a needle can be imaged in its entirety. If this needle is to be introduced into a blood vessel, it is not entirely certain that the needle is positioned in the centre of the blood vessel if only one plane is used.
In order to overcome these and similar problems, various types of transducer elements have also already been developed which comprise various rows of transducers.
Such transducer elements have already been described, for example, in WO 03/065896 A2, U.S. Pat. No. 6,261,234 B1, U.S. Pat. No. 3,888,238 A, U.S. Pat. No. 5,891,039 A and U.S. Pat. No. 4,373,533 A.
By means of a transducer element comprising several rows of transducers, it is, for example, possible to image a needle simultaneously in both said directions, so that a correct positioning thereof is greatly simplified.
However, such transducer elements are not practical for scanning, for example, small cavities (for example subclavia), whereas a small linear transducer element would be advantageous.
On the other hand, long linear transducers are often used to gain a better overview of the surrounding structures.
As transducer elements are the most expensive parts of echoscopes, it will be rare, in practice, to have all the possible uses of these transducer elements available. Therefore, a choice is often made for certain transducer elements and only one or a few transducer elements are bought, the advantages of which correspond most closely to the most frequent application.